Helical slow wave structure for a travelling wave tube to provide heat removal from the slow wave structure



Oct. 29, 1968 0. E. SOLOMON 3,408,529

HELICAL SLOW WAVE STRUCTURE FOR A VELL TO PROVIDE HEAT R TUBE ING WAVE EMOVAL FROM THE W WAVE STRUCTURE Aug. 30, 1965 Filed FIG.4.

WITNESSES |NVENTQR flail/457 M Dovad E.Solomon ,Qw f BY ATTORNEY United States Patent Ofiice HELICAL SLOW WAVE STRUCTURE FOR A TRAV- ELLING WAVE TUBE TO PROVIDE HEAT RE- MOVAL FROM THE SLOW WAVE STRUCTURE David E. Solomon, Ann Arbor, Mich., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 30, 1965, Ser. No. 483,607

6 Claims. (Cl. 3153.5)

ABSTRACT OF THE DISCLOSURE This invention relates to a traveling wave tube utilizing a helical member for a slow wave structure in which the helical conductor has a cross-section configuration such that the inner surface of the helical conductor is a curved line and the outer surface of the helical conductor is a straight line to provide a flattened outer surface. The outer flattened surface provides a larger area surface to remove heat from the conductor by means of heat conducting rods having surfaces substantially parallel to the flattened surfaces on the helix and in contact therewith.

This invention relates to traveling wave tubes and more particularly to the slow wave propagation structure and to a method of manufacturing the same.

A traveling wave tube may be considered in its broadest sense to be simply a device for providing continuous interaction between an electron beam and an electromagnetic wave so that the electromagnetic wave is amplified. The tube generally comprises an elongated evacuated envelope with an electron beam producing means provided at one end thereof for the production and projection of an electron beam along a predetermined path or axis within the envelope. A slow wave structure, usually comprising an electrical conductor in the form of a helix is provided for propagating an electromagnetic wave along the length of the envelope in an interacting relationship with the electron beam.

In high power traveling wave tubes, considerable heat is generated within the slow wave structure due to interception of the electron beam and radio frequency losses. It is therefore necessary in the higher power tubes to provide means for removing the heat from the slow wave structure. This normally requires that the contact area between the outside diameter of the helix or slow Wave structure and supporting dielectric rods be of a maximum value to permit conduction of the heat from the helix to a suitable heat sink.

One solution that has been proposed is the provision of a tape-type helix in which the conductor is rectangular in cross section to provide maximum contact between the helix and the support rods. It is found, however, that the tape-type helix permits energy to be stored between adjacent turns of the helix of a relatively high value and therefore the backward wave impedance is high. This results in the traveling wave tube being highly susceptible to oscillation and is found to be generally unstable.

Accordingly, it is a general object of this invention to provide a new and improved traveling wave tube.

It is another object to provide an improved conductor configuration for the helix in a traveling wave tube to provide maximum heat transfer therefrom and also to provide good electrical properties.

It is another object of this invention to provide a method of manufacturing an improved helix for a traveling wave tube.

Briefly, the present invention accomplishes the abovecited objects by providing a helical member in which the conductor has a cross section configuration such that the inner surface of the helical conductor is substantially circular in shape and the outer surface of the helical conductor is substantially flat. The structure is obtained by Winding a circular cross sectional configuration wire about a mandrel and then removing the outer portion of the winding to provide a flattened outer surface and circular inner surface.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a schematic representation showing the traveling wave tube embodying the present invention;

FIG. 2 is a cross sectional view taken along the line II.-II of FIG. 3;

FIG. 3 is a cross sectional view taken along the line IIIIII of FIG. 1; 7

FIG. 4 is a cross sectional view illustrating one step in the manufacture of the slow wave structure; and

FIG. 5 is a cross sectional view illustrating a second step in the manufacture of the slow 'wave structure.

Referring in detail to FIG. 1, there is illustrated a traveling wave tube which is comprised of an evacuated envelope 10. The envelope 10 consists of a tubular inner portion 11 which is of constant cross sectional area and is of a suitable material such as copper or molybdenum. An electron beam source 14 is provided at one end of the envelope 10, and is disposed within an envelope end portion 13. The end portion 13 is of a suitable material such as a glass and is sealed to the inner portion 11. The electron beam source 14 comprises at least an electron emissive cathode 17, a focusing electrode 19, and an accelerating electrode 21. These electrodes 17, 19 and 21 are connected to suitable sources of voltages which have not been shown, and collectively act to direct a beam of electrons along the axial length of the inner tubular portion 11 to the opposite end of the envelope 10 at which point is located an electron collector 23. The collector 23 is positioned transverse to the electron beam within an envelope end portion 15 located at the opposite end of the envelope 10 from the envelope end portion 13. The envelope end portion 15 may also be of glass and is sealed to the inner tubular portion 11. The collector 23 is also connected to a suitable source of potential which is not shown. A slow wave propagating means 25, for the propagation of radio frequency energy is disposed centrally within the envelope 10 and within the ma or portion of the axial length of the inner tublar portion 11 and is coaxial with and in interacting relationship wlth the major portion of the electron beam from the elec tron gun 14. Electromagnetic energy may be applied to the slow wave structure 25 by means of a coaxial coupling 29 sealed through the wall of the envelope 10 or by any other suitable system. A second coaxial coupling 31 is provided at the opposite end of the slow wave structure 25 for the removal of radio frequency energy from the slow wave structure 25.

The slow wave structure 25 is a helix formed of a suitable electrically conducting material such as tungsten. The cross sectional configuration of the conductor is illustrated in FIG. 2. The conductor is wound so that the cross sectional view of the conductor includes a curved line 26 on the interior region of the helix 25 and a straight line 28 on the exterior region of the helix. The conducting element of the helix 25 is wound to form the helix 25 having a spacing between turns suitable for the frequencies to be employed.

Positioned against the helix 25 and in thermal contact is one and preferably three or four ceramic rod members Patented Oct. 29, 1968 A 30. These rod members are substantially coextensive with the helix 25 and are disposed along the axial length of the envelope for supporting the helix within the inner envelope portion 11. The support members illustrated in the specific embodiment are substantially keystoned shaped in cross sectional to provide large area heat conductive contacts to the helix 25 and to the envelope 10. The support members 30 may be of any suitable heat conducting electrically insulating material such as alumina or beryllia.

In order to minimize the action of the electron beam of spreading to the extent that it would pass out of the interaction region and intercept the slow wave structure 25, it is necessary to provide some form of focusing means. Focusing in the present invention is provided by a magnetic field structure. This field may be achieved by providing a long annular solenoid 33 which surrounds the envelope portion 11 for substantially its entire length.

In the fabrication of the slow wave structure 25, as illustrated in FIGS. 4 and 5, a tungsten Wire of circular cross section and a suitable diameter (typically .030 inch) is wound onto a cylindrical mandrel of a suitable material such as molybdenum. In the specific embodiment the mandrel 40 has a diameter of .093 inch. The mandrel 40 with the helix 25 is then provided with a potting material 42 such as acrylic and is illustrated in FIG. 4. After the potting material 42 has set, the glass tubing 44 and the plugs 46 are removed. The mandrel 40 is then positioned in a suitable grinding machine and the outer portion of the potting material 42 is removed by grinding until the helix 25 is exposed. The mandrel is then positioned in a centerless grinding machine and the outside diameter of the mandrel 40 and helix 25 is reduced to a diameter of about .111 inch. The helix 25 is then chemically cleaned. The helix 25 is then given a rhodium strike and then a copper coating of about .001 inch in thickness. The potting material 42 is then removed by using ultrasonic techniques. The helix 25 may then easily be removed from the mandrel 40 and stored prior to assembly to the mounting spacers and assembly into the tube. In this manner, the helix 25 is fabricated by an economical method to provide a helix 25 in which the cross section of the conductor is an internal curved line and an outer straight line.

It is obvious that the helix 25 may be secured by several techniques to the mandrel 40. It is only necessary that it be secured so as to withstand the grinding step.

While the invention has been shown and described in what is presently considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

1 claim as my invention:

1. A traveling wave tube comprising an envelope, an electron gun positioned at one end of said envelope to direct a beam of electrons therethrough, a collector at the opposite end of said envelope to collect the electrons from said electron gun, a slow wave propagating tubular structure within said envelope intermediate said electron gun and said collector to propagate electromagnetic waves at a rate such that an interaction with the electron beam is obtained, said slow wave structure formed of a helically wound conductor, said conductor having a cross sectional configuration defined by a curved line on the inner surface of said slow wave structure and a straight line on the outer surface of said slow wave structure, said conductor having said cross sectional configuration over a substantial portion of the length of said conductor and support members positioned between the straight line portion of the outer surface of said slow wave structure and said envelope for supporting said slow wave structure Within said envelope, said support members in contact with a substantial portion of said straight line portion providing conduction of heat from said slow wave structure to said envelope.

2. A traveling wave tube comprising an envelope, an electron gun positioned at one end of said envelope to direct a beam of electrons therethrough, a collector electrode at the opposite end of said envelope to collect the beam of electrons from said electron gun, an elongated slow wave propagating structure within said envelope between said electron gun and said collector to propagate electromagnetic waves at a rate such that an interaction with the electron beam is obtained, said slow wave structure formed of a helically wound conductor, said conductor having at least one portion having cross sectional configuration defined by a curved line on the inner surface of said slow wave structure and a straight line on the outer surface of said slow Wave structure and a support member positioned between the outer surface of said slow wave structure in contact with said straight line outer surface of said conductor and said envelope.

3. A traveling wave tube comprising a tubular envelope, an electron gun positioned at one end of said envelope andadapted to direct a beam of electrons therethrough, a collector at the opposite end of said envelope adapted to collect the electrons from said electron gun, a slow wave propagating tubular structure within said envelope between said electron gun and said collector and adapted to propagate electromagnetic waves at a rate such that an interaction with said electron beam is obtained, said slow wave propagating structure including a conductive element having a section having a cross sectional configuration defined by a curved line surface on the inner surface of said slow wave structure and a straight line on the outer surface of said slow wave structure and members positioned between said section of said slow wave structure and said envelope and in contact with the straight line portion for conducting heat from said slow wave structure to said envelope.

4. A traveling wave tube comprising an envelope, an electron gun positioned at one end of said envelope to generate a beam of electrons, a collector electrode at the opposite end of said envelope to collect the electrons from said electron gun, a slow wave propagating structure within said envelope intermediate said electron gun and said collector adapted to propagate electromagnetic waves at a rate such that an interaction with said electron beam is obtained, said slow wave propagating structure including a conductive element having a cross sectional configuration defined by a curved line portion on the inner surface of said slow wave structure and a straight line portion on the outer surface of said slow wave structure to provide a flattened outer surface and heat conductive members positioned between said flattened outer surface of said slow wave structure and said envelope for conducting heat from said slow wave structure to said envelope, said members having inner surfaces parallel to and in contact with said flattened outer surface of said slow wave structure.

5. A traveling wave tube comprising an envelope, an electron gun positioned at one end of said envelope to generate a beam of electrons, a collector at the opposite end of said envelope to collect the electrons from said gun, a tubular member within said envelope intermediate said electron gun and said collector adapted to propagate electromagnetic waves at a rate such that an interaction with the electron beam is obtained, said tubular member formed of a helically wound conductor, said conductor member having a cross section to provide a cylindrical surface on the inner region of said tubular member and a flattened surface on the outer region of said tubular member and a support member positioned between the flattened surface of said conductor and said envelope with the inner surface of support member substantially parallel to and in contact with said flat surface for supporting said tubular member within said envelope and providing conduction of heat from said tubular member to said envelope.

6. A traveling wave tube comprising a tubular envelope portion, an electron gun positioned at one end of said envelope portion to generate a beam of electrons therethrough, a collector at the opposite end of said envelope portion adapted to collect said beam of electrons, a tubular member within said envelope intermediate said electron gun and said collector adapted to propagate electromagnetic waves at a rate such that an interaction with the electron beam is obtained, said tubular member including a conductive member, said conductor member having a semi-circular cross-section to provide a circular inner surface within said tubular member and flattened outer surface on the said tubular member and a heat conductive member positioned between the flattened outer surface of said conductive member and said envelope for supporting said tubular member within said envelope and providing conduction of heat from said tubular member to said envelope, said heat conductive member having a surface substantially parallel to said flattened surface and in contact therewith.

References Cited UNITED STATES PATENTS 3,089,975 4/1963 Washburn 3153.6 3,121,819 2/1964 'Wilmarth 315-3.6 3,273,081 9/1966 Itzkan 3153.6 X

ELI LIEBERMAN, Primary Examiner. S. CHATMON, JR., Assistant Examiner. 

